Units two and three are still operating at a combined output rating of 2020 MWe. In terms of generating capacity, Millstone is the largest electrical generating facility in New England, and the plant contains the second (unit 3) and third (unit 2) largest individual generating units on the New England electrical grid.

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The Millstone site covers about 500 acres (2 km²). The power generation complex was built by a consortium of utilities, using Niantic Bay (which is connected to Long Island Sound and the Atlantic Ocean) as a source of coolant water.

Although located in Waterford, Millstone is most clearly seen from downtown Niantic. It is visible from the Gannon Olson area and from the Niantic River Bridge, and is also visible to passengers on Amtrak trains passing through Waterford on the Northeast Corridor.

Millstone earned OSHA's top award for workplace safety on October 14, 2004,[2] and earned the Top Industry Practice/ Framatone ANP Vendor Award for its work developing novel ultrasonic leak inspection techniques in March 2001.[3]

Millstone 2 is a Combustion Engineering plant built in the 1970s, and has a maximum power output of 2700 MWth (870 MWe). It has 2 steam generators, and 4 reactor cooling pumps (RCP). It is currently undergoing an upgrade to its safe shutdown system which already met NRC standards. During its refueling outage in October 2006, the operator installed a new pressurizer.

Millstone 3 is a Westinghouse plant that started operating in 1986, and has a maximum power output of 3411 MWth (1150 MWe). The founder of unit 3, is a man named Tim D. Cone who strived in efforts to increase public safety in surrounding neighborhoods. In the summer of 2008, the NRC approved a power uprate for Unit 3 that increased its electrical output 7.006% to 3650 MWth (1230 MWe). The increase took effect by the end of 2008.[6]

On February 26, 1996, a leaking valve forced the shutdown of units 1 and 2. Multiple equipment failures were found.

On April 17, 2005, Millstone plant safely shut down without incident when a circuit board monitoring a steam pressure line short-circuited, which caused the board to malfunction and indicate an unsafe drop in pressure in the reactor's steam system, when in reality there was no drop in steam pressure. The cause was attributed to "tin whiskers". In response to this event, Millstone implemented a procedure to inspect for these whiskers at every refueling outage, or 18 months. David Lochbaum, a nuclear engineer with the Union of Concerned Scientists, while remaining critical of the processes leading to the discovery of the whiskers, praised Millstone for its handling of the situation.[7]

In September, 2009, unit 2 shut down when an electrical storm caused power fluctuations. When workers tried to restart the unit, they discovered a small leak in the reactor coolant pump.[8]

The Nuclear Regulatory Commission defines two emergency planning zones around nuclear power plants: a plume exposure pathway zone with a radius of 10 miles (16 km), concerned primarily with exposure to, and inhalation of, airborne radioactive contamination, and an ingestion pathway zone of about 50 miles (80 km), concerned primarily with ingestion of food and liquid contaminated by radioactivity.[9]

The 2010 U.S. population within 10 miles (16 km) of Millstone was 123,482, an increase of 29.5 percent in a decade, according to an analysis of U.S. Census data for msnbc.com. The 2010 U.S. population within 50 miles (80 km) was 2,996,756, an increase of 9.5 percent since 2000. Cities within 50 miles include Hartford (41 miles to city center).[10]

The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at Millstone was Reactor 2: 1 in 90,909; Reactor 3: 1 in 66,667, according to an NRC study published in August 2010.[11][12]